3-hydroxy-3-methylhexanoic acid and 3-methyl-2-hexanoic acid detection as identifiers to monitor human presence

ABSTRACT

Various embodiments are described relating to devices and methods for detecting local human presence by olfactory reception of volatile organic compound (VOC) molecules dispersed in air. Such devices include a chamber inlet, a trap, a sensor and a communicator. The inlet receives the air that contains the VOC molecules, a trap for capturing the VOC molecules in the air. The sensor detects at least a threshold quantity of at least one of 3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H) acid among the VOC molecules. The communicator provides notification of the threshold quantity. The methods include operations to receive the air, capture the molecules in the air, detect the 3H3MH and 3M2H acids, and signal notification of that detection.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION

This invention relates to chemical detection of human presence.

BACKGROUND

Government and private officials often have responsibility forcontrolled areas subject to restrictive access to authorized persons.Such officials may employ various techniques to detect human presence.These tools generally depend on human activity to present a detectablesignal.

Human activity may trigger a sensor based on various stimuli. Forexample, skeletal-muscular physical motion may form pressure gradientsin the local environment, either the surrounding air or through theground. For sufficiently intense pressure gradients, such motion mayregister motion or audio signals. Complimentarily, metabolic activitymay yield a thermal contrast between the temperatures of a human bodyand the ambient surroundings.

SUMMARY

Various embodiments are described relating to devices and methods fordetecting local human presence by the reception and detection ofhuman-specific volatile organic compound (VOC) molecules dispersed inair. According to an example embodiment, such devices include a chamberinlet, a trap, a sensor and a communicator. The inlet receives the airthat contains the human-specific VOC molecules, a trap for capturing theVOC molecules in the air.

The sensor detects at least a threshold quantity of at least one of3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H)acid among the VOC molecules. The communicator provides notification ofthe threshold quantity. The methods include operations to receive theair, capture the molecules in the air, detect the 3H3MH and 3M2H acids,and signal notification of that detection.

According to an example embodiment, the trap includes a sieve forcapturing the VOC molecules from the air and a heater for releasing thecaptured VOC molecules from the sieve. In addition, the sensor comprisesa chemical analyzer such as, for example, an ion-mobility spectroscope,a gas chromatograph, a gas chromatograph plus a mass spectroscope, and aflame ionization spectroscope. The corresponding exemplary methodemploys chemical detection of the 3H3MH and 3M2H acids.

According to another example embodiment, the trap comprises a filterthat includes polyacrylamide fibers for capturing the VOC molecules fromthe air. In addition, the sensor comprises an electrode for respondingto a physical property change in the polyacrylamide fibers. Thisphysical property change, such as electrical characteristics, is causedby at least one of the 3H3MH and 3M2H acids in the captured VOCmolecules. The corresponding exemplary method employs detection ofcharacteristic changes in the filter's electrical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other features and aspects of various exemplaryembodiments will be readily understood with reference to the followingdetailed description taken in conjunction with the accompanyingdrawings, in which like or similar numbers are used throughout, and inwhich:

FIG. 1 is a diagram illustrating an olfactory detection system accordingto a chemical example embodiment;

FIG. 2 is a diagram illustrating an olfactory detection system accordingto an electrical example embodiment;

FIG. 3 is a flow diagram illustrating a logical sequence of operationsfor olfactory detection of human presence according to an exampleembodiment; and

FIG. 4 is a flow diagram illustrating a logical sequence of operationsfor olfactory detection of human presence according to an exampleembodiment.

DETAILED DESCRIPTION

Motion and thermal detectors require either physical or metabolicactivity that cannot distinguish between human presence and non-humanstimuli on a consistent or systematical basis. Consequently, sensorindication of movement or thermal contrast may result in false alarmsthat unproductively expend resources that operatives prefer to conserve.Thus, various exemplary embodiments describe techniques for exploitinghuman characteristics that exhibit unique and detectable manifestations.

Human skin, especially in axillary (i.e., armpit) regions, producesperspiration secretions whose molecules can be truncated by bacteria toproduce hexanoic acids that represent volatile organic compound (VOC)molecules. These VOC molecules produce a recognizable odor and representa uniquely human chemical signature, at least in detectable quantities.The odor produced by the VOC molecules can be sensed by olfactoryreceptors. The VOC molecules, as represented by hexanoic acids, include3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H)acid. After being captured, these VOC molecules can be heated toincrease volatility for spectroscopic detection.

FIG. 1 is a diagram illustrating a VOC detection system 100 according toan example embodiment. The system 100 includes a pair of hollowchambers, represented by cylindrical tubes. The first chamber 110 isdivided into an inlet portion 112 and a first filter portion 114 and afirst convection portion 116. The second chamber 120 is divided into asecond convection portion 122, a heater portion 124, a second filterportion 126, and an analysis portion 128.

The system 100 further includes a communicator 130. Upon detection ofthreshold-triggering quantities of 3H3MH and/or 3M2H acids, thecommunicator or signaler 130 transmits a wireless signal 132 to a remotereceiver (not shown) for intrusion and/or threat assessment.

A person 140 within detection vicinity of the system 100 releases VOCmolecules 142 into the ambient air 144, A first fan 117 within the firstconvection portion 116 drives the air 144 into the chamber 110. Themolecules 142 in the air 144 enter the inlet portion 112 and pass into asieve 115 disposed within the first filter portion 114 at a firstposition. The sieve 115 serves to capture or trap the molecules 142 byfiltering the air 144 passing therethrough.

In various exemplary embodiments, the sieve 115 is a polymeric filterthat chemically binds to the molecules 142, thereby capturing them inthe sieve 115. A transfer mechanism 118 (shown symbolically) may removethe sieve 115 from its first position in the first filter portion 114 toa second position in the second filter portion 126. Alternatively, thesieve 115 may be transferred manually from its first to second filterpositions.

The second convection portion 122 includes a second fan 123 with whichto blow air 146 over the sieve 115 disposed at the second position. Aheater 125 in the heater portion 124, in cooperation with the second fan123, volatilizes and releases the trapped molecules 142 on the sieve 115at the second position. The air 146 carries these molecules 142 byconvection to the analysis portion 128. The second fan 123 and theheater 125 may be disposed preferably upstream of the filter's secondposition.

The analysis portion 128 includes a chemical analyzer 129 to evaluatethe molecules 142 for the presence of 3H3MH and/or 3M2H acids. Thresholddetection determines human presence in the vicinity of the system 100.In various exemplary embodiments, the chemical analyzer 129 may be anyof an ion-mobility spectroscope, a gas chromatograph, a gaschromatograph plus a mass spectroscope, or a flame ionizationspectroscope. All of these analyzers are available as commercialoff-the-shelf (COTS) devices.

FIG. 2 is a diagram illustrating a VOC detection system 200 according toan example embodiment. The system 200 includes a hollow chamber 210,represented by a cylindrical tube, divided into an inlet portion 212, afilter portion 214, a convection portion 216 and an outlet portion 218.

A person 140 within the detector's vicinity releases VOC molecules 142into the ambient air 144. A fan 217 within the convection portion 216drives the air 144 with molecules 142 towards the chamber 210. Themolecules 142 in the air 144 enter the inlet portion 212 and passthrough a filter 215 disposed within the filter portion 214.

The filter 215 may include an electrode circuit 217 to sense changes infilter capacitance, conductance and/or light emission. Such physicalcharacteristics are affected for detection by the electrode circuit 217only when the filter 215 is saturated with 3H3MH and/or 3M2H acids,whereupon the communicator 130 transmits the wireless signal 132 to aremote receiver (not shown) for intrusion and/or threat assessment. Thewireless signal 132 represents a radio signal within the electromagneticspectrum, such as, but not limited to, radio, microwave and infraredfrequencies.

In various exemplary embodiments, the filter 215 may include “memory”polymers, such as polyacrylamide. Such memory polymers can be producedvia electrospinning techniques. By judiciously incorporating selectedchemical additives or “dopants” to the polymer liquid prior to beingelectrospun, the filter 215 can respond to the binding of 3H3MH and/or3M2H acids by changes in electrical conductance and/or electricalcapacitance.

Dopants for enabling such property change detection by the electrode 217include electrically conductive metal nanoparticles (particles whosediameter is less than 100 nanometers), such as gold, silver or copper,and/or electro-conductive polymers such as polyanilline. Alternatively,in response to binding with the molecules 142 the filter 215 can emitvisible light 219 in response to the VOC binding. Dopants for enablingsuch light emission by the filter 215 include any semi-conductingmaterial such as doped silicon. The light 219 may provide a visualindication of threshold quantities of the molecules 142 for furtherinvestigation. The light 219 may be transmitted to an eye-piece orthrough fiber optics to a remote monitoring station, or be used totrigger a radiofrequency signal by wireless transmission.

In various exemplary embodiments, the filter 215 may be exchanged withanother filter, after the initially installed filter becomes saturatedor to select an alternate particle size for transmission. The filter 215may be connected to a tray or carrousel 220 having a series of filters215. The tray 220 may rotate about a carrousel center 222, as shown, toexchange filters 215 mounted on spokes 224 and/or connected along a rim226. Alternatively, the tray 220 may translate as a conveyor belt 228 toexchange filters 215. The filter 215 may be inserted through a slot 230within the filter portion 214.

FIG. 3 is a flow diagram illustrating an exemplarily process 300 oflogical operations for olfactory detection of the VOC molecules 142 toindicate presence of the person 140. The process begins with at step 310and proceeds to blowing the air 144 towards a sieve at step 320. The VOCmolecules 142 in the air 144 adhere to the sieve 115 at step 330. Theheater 121 applied to the sieve 115 releases the molecules 142 at step340.

The chemical analyzer 129 receives and analyzes the molecules 142 atstep 350 to determine at step 360 whether threshold quantities of 3H3MHand/or 3M2H acids are present. Upon such chemical detection, thecommunicator 130 transmits the signal 132 at step 370 to indicatepresence of the person 140. Otherwise, or at the conclusion of signaltransmission, the process terminates at step 380.

FIG. 4 is a flow diagram illustrating another exemplary process 400 oflogical operations for olfactory detection of the VOC molecules 142 toindicate presence of the person 140. The process begins with at step 410and proceeds to blowing the air 144 towards a filter 215 at step 420.The VOC molecules 142 in the air 144 adhere to the filter 215 at step430. The electrode circuit 217 connected to the filter 215 evaluatescharacteristic changes to electrical properties of the filter 215 atstep 440 caused by saturation of the VOC molecules 142 to determine atstep 450 whether threshold quantities of 3H3MH and/or 3M2H acids arepresent.

Upon such electrical detection, the communicator 130 transmits thesignal 132 at step 460 to indicate presence of the person 140. Afterreaching VOC molecular saturation, the filter 215 can changed at step470. In the absence of such detection at step 450, or at the conclusionof signal transmission, the process terminates at step 480.

While certain features of the embodiments of the invention have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the embodiments.

1. A device for detecting local human presence by reception anddetection of human-specific volatile organic compound (VOC) moleculesdispersed in air, the device comprising: a chamber inlet for receivingthe air that contains the VOC molecules; a trap for capturing the VOCmolecules in the air; a sensor for detecting at least a thresholdquantity of 3-hydroxy-3-methylhexanoic (3H3MH) acid among the VOCmolecules; and a communicator for providing notification of thethreshold quantity.
 2. The device of claim 1, wherein the chamber inletincludes a fan for drawing the air that contains the VOC molecules intothe trap.
 3. The device of claim 1, wherein the trap comprises: a sievefor capturing the VOC molecules from the air; and a heater for releasingthe captured VOC molecules from the sieve.
 4. The device of claim 3,wherein the trap further comprises a fan for drawing the released VOCmolecules to the sensor.
 5. The device of claim 3, wherein the sieve isa polymeric filter that chemically binds to the VOC molecules.
 6. Thedevice of claim 4, wherein the sieve captures the VOC molecules at afirst position downstream of the chamber inlet and releases the VOCmolecules from second position upstream of the sensor.
 7. The device ofclaim 6, wherein the fan and the heater are disposed upstream of thesecond position.
 8. The device of claim 1, wherein the sensor comprisesa chemical analyzer selected from the group consisting of anion-mobility spectroscope, a gas chromatograph; a gas chromatograph plusa mass spectroscope, and a flame ionization spectroscope.
 9. The deviceof claim 1, wherein the communicator is a wireless transmitter.
 10. Thedevice of claim 1, wherein the trap comprises a filter for capturing theVOC molecules from the air, the filter including polyacrylamide fibers;and the sensor comprises an electrode for responding to a physicalproperty change in the polyacrylamide fibers caused by the 3H3MH acid inthe captured VOC molecules.
 11. The device of claim 10, wherein thephysical property change is at least one of electrical conductivity andelectrical capacitance.
 12. The device of claim 10, wherein the physicalproperty change produces visible light emission for transmission to thecommunicator.
 13. The device of claim 10, wherein the polyacrylamidefibers are doped with at least one of electrically-conductive metalparticles and an electrically conductive polymer.
 14. The device ofclaim 10, wherein the polyacrylamide fibers are doped withelectrically-conductive metal particles.
 15. The device of claim 14,wherein the electrically-conductive metal particles are nanoparticlesfrom the group consisting of gold, silver and copper.
 16. The device ofclaim 3, wherein the trap includes a fan for drawing the released VOCmolecules to the sensor and a filter for capturing the VOC moleculesfrom the air, the filter including polyacrylamide fibers, the sensorcomprises an electrode for responding to a physical property change inthe polyacrylamide fibers caused by the 3H3MH acid in the captured VOCmolecules.
 17. The device of claim 16, wherein the polyacrylamide fibersare doped with at least one of electrically-conductive metal particlesand an electrically conductive polymer.
 18. The device of claim 17,wherein the electrically-conductive metal particles are nanoparticlesfrom the group consisting of gold, silver and copper.
 19. The device ofclaim 16, wherein the polyacrylamide fibers are doped with polyanniline.20. The device of claim 1, wherein the sensor also detects a thresholdquantity of 3-methyl-2-hexanoic (3M2H) acid among the VOC molecules. 21.The device of claim 10, wherein the electrode responds to a physicalproperty change in the polyacrylamide fiber caused by 3M2H acids in thecaptured VOC molecules.
 22. The device of claim 16, wherein theelectrode responds to a physical property change in the polyacrylamidefibers caused by 3M2H acids in the captured VOC molecules.